The Sword is an enormous silver sword, shaped like a typical arming sword from Jonathan Shadowhunter's period. It has a straight double-edged blade and a one-handed hilt with an elaborate design of outspread wings, emerging from the point where blade meets handle.
According to Clary Fray, the Sword is agonizing to bear. Its weight and coldness, giving the holder a tingling sensation, as if hooks embed their hands onto the sword, contributes to the mental pain truth compulsion it triggers.
The Soul-Sword is primarily used to compel Nephilim to tell the truth, mostly during trials. Shadowhunters who wish to have their claims tested and proved may submit themselves to "trial by the Sword," during which a suitable judge, often a Silent Brother, sometimes the Consul or Inquisitor, wields the sword and places it in the hands of the deponent, where it adheres and cannot be removed until the judge wills it.
The Sword can also have a dark purpose, if intended. Originally, the alliance of the Soul-Sword is seraphic, its power drawn from Angel Raziel himself. However, Valentine Morgenstern discovered a way to reverse the alliance from angelic to demonic, through a process called the Ritual of Infernal Conversion, where the Sword is seethed until red-hot and cooled four times in the blood of Downworld children: a child of Lilith, a child of the moon, a child of the night, and a child of the fey. With its demonic alliance, the Sword can be used to summon demons and allows its bearer to have control over them.
Some weeks after, it was stolen by Valentine Morgenstern in his attack of the Silent City with the help of the Greater Demon Agramon, the evening before Jace's trial by the Sword. Valentine stole it for the Ritual of Infernal Conversion, which he was able to successfully perform, allowing him to build an army of demons to summon weeks later at Idris. He also used the Sword to kill Jace and summon Raziel.